1. Field of the Invention
The present invention relates to end turn support arrangements for dynamoelectric machines and in particular to a novel filler material for supporting the coil end portions at the diamond area of a dynamoelectric machine.
2. Description of the Prior Art
In the dynamoelectric machine art there continues to be a need for improving the support arrangements for the end turn portions of the winding coils extending from the ends of the stators of dynamoelectric machines such as large turbine generators. Manifestly, the stresses imposed during operation, particularly those caused by vibration, result in wear of coil insulation and fatigue cracking in series and copper strand phase connections. Many proposals have been made in the past in an effort to solve these long standing problems an examples of prior art arrangements are illustrated in U.S. Pat. Nos. 3,949,256, 3,949,257, 4,379,243 and 4,488,079, the entireties of the disclosures of which are hereby specifically incorporated herein by reference. Other proposals have included packing the entire end turn area with a thixotropic, curable potting resin such as an epoxy, a polyester or polyurethane material.
More recently, the problems inherent in the prior art have been addressed by a support arrangement for the diamond area of a dynamoelectric machine which includes spacer blocks disposed within a resin filler and which have a specific volume and coefficient of thermal expansion to prevent excessive build up of temperature during curing of the resin and decrease the overall coefficient of thermal expansion of the filler material and adjust the thermal expansion characteristics thereof so that the latter more closely matches the thermal expansion characteristics of the coils. Such development is disclosed and claimed in commonly assigned, co-pending application Ser. No. 091,223 filed Aug. 31, 1987.
The subject matter of the foregoing application addresses a number of problems which are encountered when using resin fillers. Among such problems is that fillers, and in particular the epoxy resins which have the best mechanical properties for the application, generally have a coefficient of thermal expansion which appears to be approximately 4 times as great as the apparent coefficient of thermal expansion of the end turns themselves. As set forth in said prior application, the entirety of the disclosure of which is hereby specifically incorporated by reference, the coefficients of thermal expansion of the various components of the end turn arrangements of dynamoelectric machines are difficult to calculate with any mathematical exactitude, but the general result of a significant mismatch between the coefficients of the filler material and of the end turn windings is often a debonding of the resin filler from the windings.
Another problem addressed by said prior application is that when potting resin type materials are used, the curing reaction is generally highly exothermic, and when the volume of the curing material is too great, hot spots sufficient to actually destroy the resin may develop internally.
Another problem encountered when resin fillers are used, is that during the initial installation of the end turn filler material, the same is injected into the end turn area in a generally liquid state. Although the viscosity and thixotropy of the resin may be controlled to some degree by methodology which is presently known, the resin still tends to sag under its own weight and drip out of the winding area during cure. Moreover, even after curing the cured resins may have semi-rigid characteristics which sometimes allow internal flexing and independent vibration.
The present invention is aimed at the provision of a novel semi-rigid spacer for the diamond area of the dynamoelectric machine which addresses many of the problems encountered when using prior art resin fillers. In particular the invention provides means and a method which facilitate the holding of the resin in place after injection and during the curing stage. The present invention also provides means for increasing the effective stiffness of the filler material and controlling the linear thermal coefficient expansion of the filler resin.